System and method for compressor capacity modulation in a heat pump

ABSTRACT

A system and method is provided to control and operate a compressor to have two or more discrete output capacities in response to an outdoor temperature measurement. During operation of the compressor in an air conditioning or cooling mode, the compressor has a first output capacity in response to the outdoor temperature being greater than a first temperature setpoint and the compressor has a second output capacity in response to the outdoor temperature being less than a second temperature setpoint. During operation of the compressor in a heating mode, the compressor has different output capacities based on the outdoor ambient temperature.

BACKGROUND OF THE INVENTION

The present invention relates generally to a control system for acompressor. More specifically, the present invention relates to acapacity modulation system for a compressor that can automaticallyadjust the capacity of the compressor in a heat pump during a heatingoperation.

Frequently, motors for driving compressors in heating, ventilation andair conditioning (HVAC) systems are designed to operate from standardline (main) voltages and frequencies (e.g., 230 V, 60 Hz) that areavailable at the location where the HVAC system is being operated. Theuse of line voltages and frequencies results in the motor being limitedto one operating speed that is based on the input frequency to themotor. The operation of the motor at one speed, in turn, results in thecompressor being limited to a single output capacity. Furthermore,motors that require their own controller or electronic drive, e.g.,switched reluctance motors, cannot be used for these HVAC systems, assuch motors cannot operate directly from standard (main) voltages andfrequencies.

One problem with the compressor being limited to a single outputcapacity is that the compressor, especially a reciprocating compressor,has a limited heating capacity at reduced outdoor ambient temperatures.This limited heating capacity produced by the compressor adverselyaffects the EER (Energy Efficiency Rating) and HSPF (Heating SeasonPerformance Factor) of any system incorporating the compressor duringtesting and in subsequent operation of the system. Furthermore, thelimited heating capacity output of the compressor at reduced outdoorambient temperatures requires additional (and more costly) heatingtechniques to be used to maintain a setpoint temperature in an enclosedspace.

Therefore, what is needed is a cost-effective, efficient and easilyimplemented system to boost the heating capacity of a compressor atreduced outdoor ambient temperatures.

SUMMARY OF THE INVENTION

An embodiment of the present invention is directed to a method formodulating capacity in a compressor for a heat pump operating in aheating mode. The method includes providing a controller configured toprovide a plurality of discrete output frequencies to a motor for thecompressor of the heat pump, measuring an outdoor ambient temperature,selecting a discrete output frequency of the plurality of discreteoutput frequencies in response to the measured outdoor ambienttemperature, operating the motor at the selected discrete outputfrequency and a corresponding voltage to produce a corresponding outputcapacity for the compressor. The selected discrete output frequency ofthe plurality of discrete output frequencies is inversely related to themeasured outdoor ambient temperature.

Another embodiment of the present invention is directed to an HVAC&Rsystem having a compressor, a condenser arrangement and an evaporatorarrangement connected in a closed refrigerant loop. The HVAC&R systemalso has a motor connected to the compressor to power the compressor anda control system to power the motor. The motor is configured to operateat a plurality of output speeds to generate a plurality of outputcapacities from the compressor. The control system is configured toprovide the motor with a plurality of discrete output frequencies togenerate the plurality of output speeds in the motor. The HVAC&R systemfurther includes a sensor arrangement to measure a parametercorresponding to an outdoor ambient temperature and to provide a signalto the control system with the measured parameter. Finally, in responseto the HVAC&R system operating in a heating mode, the control system isconfigured to provide a discrete output frequency of the plurality ofdiscrete output frequencies to the motor in response to the measuredparameter and the provided discrete output frequency is increased inresponse to a decrease in the outdoor ambient temperature to generate anincrease in the output capacity of the compressor.

Still another embodiment of the present invention is directed to amethod for controlling capacity in a compressor of an HVAC&R system. Themethod includes providing a controller configured to provide a pluralityof discrete output frequencies to a motor for the compressor, measuringan outdoor ambient temperature, and determining whether the HVAC&Rsystem is operating in a heating mode or a cooling mode. In response tothe HVAC&R system operating in a heating mode, executing a heating modeoperation process that includes selecting a discrete heating mode outputfrequency of the plurality of discrete heating mode output frequenciesin response to the measured outdoor ambient temperature, operating themotor at the selected discrete heating mode output frequency and acorresponding voltage to produce a corresponding output capacity for thecompressor, and wherein the selected discrete heating mode outputfrequency of a plurality of discrete heating mode output frequenciesprogressively increases in response to the measured outdoor ambienttemperature decreasing to provide an increase in the output capacity ofthe compressor. In response to the HVAC&R system operating in a coolingmode, executing a cooling mode operation process that includes comparingthe measured outdoor ambient temperature to at least one predeterminedtemperature setpoint, selecting a discrete cooling mode output frequencyof a plurality of discrete cooling mode output frequencies based on thecomparison of the measured outdoor ambient temperature and the at leastone predetermined temperature setpoint, operating the motor at theselected cooling mode discrete output frequency and a correspondingvoltage to produce a corresponding output capacity for the compressor,and wherein the selected discrete cooling mode output frequency of theplurality of discrete cooling mode output frequencies progressivelyincreases in response to the measured outdoor ambient temperatureincreasing to provide an increase in the output capacity of thecompressor.

One advantage of the present invention is increased system performance,efficiency and capacity control at reduced outdoor ambient temperaturesin both heating and cooling modes of operation.

A further advantage of the present invention is that the capacitymodulation of the compressor is invisible when compared to a standardsingle stage compressor.

Another advantage of the present invention is that the motor drive canbe used for different types of input power (i.e., multi-voltage andsingle phase or three phase) and with different types of compressors andmotors.

An additional advantage of the present invention is that no additionalstarting components are needed, e.g., start capacitors and/or relays.

Another advantage of the present invention is that the compressor outputcan be tuned to a specific system incorporating the compressor.

Other features and advantages of the present invention will be apparentfrom the following more detailed description of the preferredembodiment, taken in conjunction with the accompanying drawings whichillustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematically a general configuration of the presentinvention.

FIG. 2 illustrates schematically an embodiment of a variable speed driveof the present invention.

FIGS. 3A and 3B illustrate schematically a refrigeration system that canbe used with the present invention.

FIG. 4 illustrates schematically an embodiment of a control drive of thepresent invention.

FIG. 5 illustrates a flow chart of one embodiment of the capacitycontrol process of the present invention for cooling mode operation.

FIG. 6 illustrates a flow chart of another embodiment of the capacitycontrol process of the present invention for heating mode operation.

FIG. 7 illustrates system output capacities during heating modeoperation.

Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates generally a system configuration of the presentinvention. An AC power source 102 supplies electrical power to a motordrive 104, which powers a motor 106. The motor 106 is preferably used todrive a corresponding compressor of a HVAC&R system (see generally,FIGS. 3A and 3B). The AC power source 102 provides single phase ormulti-phase (e.g., three phase), fixed voltage, and fixed frequency ACpower to the motor drive 104. The motor drive 104 can accommodatevirtually any AC power source 102, preferably an AC power source 102that can supply an AC voltage or line voltage of 187 V, 208 V, 230 V,380 V, 460 V, or 600 V, at a line frequency of 50 Hz or 60 Hz.

The motor drive 104 can be a variable speed drive (VSD) or variablefrequency drive (VFD) that receives AC power having a particular fixedline voltage and fixed line frequency from the AC power source 102 andprovides power to the motor 106 at a desired voltage and desiredfrequency (including providing a desired voltage greater than the fixedline voltage and/or providing a desired frequency greater than the fixedline frequency), both of which can be varied to satisfy particularrequirements. Alternatively, the motor drive 104 can be a “stepped”frequency drive that can provide a predetermined number of discreteoutput frequencies and voltages, i.e., two or more, to the motor 106.

FIG. 2 illustrates one embodiment of the motor drive (VSD) 104 of thepresent invention. The VSD 104 can have three stages: aconverter/rectifier stage 202, a DC link/regulator stage 204 and anoutput stage having an inverter 206. The converter 202 converts thefixed line frequency, fixed line voltage AC power from the AC powersource 102 into DC power. The DC link 204 filters the DC power from theconverter 202 and provides energy storage components. The DC link 204can be composed of capacitors and inductors, which are passive devicesthat exhibit high reliability rates and very low failure rates. Theinverter 206 converts the DC power from the DC link 204 into variablefrequency, variable voltage power for the motor 106. Furthermore, it isto be understood that the converter 202, DC link 204 and inverter 206 ofthe VSD 104 can incorporate several different components and/orconfigurations so long as the converter 202, DC link 204 and inverter206 of the VSD 104 can provide the motor 106 with appropriate outputvoltages and frequencies.

The motor drive (VSD) 104 can be used to slowly increase (ramp-up) thespeed and/or torque of the motor 106 during a start-up of the motor 106.The ramping-up of the speed and/or torque during start-up can minimizehydraulic forces in the compressor, if liquid refrigerant is present inthe oil sump, thereby eliminating the need to preheat oil in thecompressor before start-up with a crankcase oil heater.

In addition, in one embodiment of the present invention, the motor 106can operate from a nominal voltage that is less than the fixed voltageprovided by the AC power source 102 and output by the motor drive 104.By operating at a voltage that is less than the fixed AC voltage, themotor 106 is able to continue operation during times when the fixedinput voltage to the motor drive 104 fluctuates. For example, the motorcan be nominally optimized for approximately 187 V (i.e., the lowestexpected voltage for this type of equipment) so any low or high voltageexcursions from the normal line voltages are absorbed by the drive and aconstant voltage is applied to the motor. This “multivoltage input andoutput voltage regulator” feature permits one drive to operate onvirtually any available AC power source. As is known, the nominal outputvoltage value of the drive is frequency and load dependent and can varybased on those needs.

As shown in FIGS. 3A and 3B, the heating, ventilation, air conditioningand refrigeration (HVAC&R) system 300 includes a compressor 302, acondenser arrangement 304, and an evaporator arrangement 306 or acompressor 302, a reversing valve arrangement 350, an indoor unit 354and an outdoor unit 352. The system 300 can be operated as an airconditioning only system, where the evaporator arrangement 306 ispreferably located indoors, i.e., as indoor unit 354, to provide coolingto the indoor air and the condenser arrangement 304 is preferablylocated outdoors, i.e., as outdoor unit 352, to discharge heat to theoutdoor air. The system can also be operated as a heat pump system withthe inclusion of the reversing valve arrangement 350 to control anddirect the flow of refrigerant from the compressor 302. When the heatpump is operated in an air conditioning mode, the reversing valvearrangement 350 is controlled for refrigerant flow as described abovefor an air conditioning system. However, when the heat pump is operatedin a heating mode, the flow of the refrigerant is in the oppositedirection from the air conditioning mode and the condenser arrangement304 is preferably located indoors, i.e., as indoor unit 354, to provideheating of the indoor air and the evaporator arrangement 306, i.e., asoutdoor unit 352, is preferably located outdoors to absorb heat from theoutdoor air.

Referring back to the operation of the system 300, whether operated as aheat pump or as an air conditioner, the compressor 302 is driven by themotor 106 that is powered by VSD 104. The VSD 104 receives AC powerhaving a particular fixed line voltage and fixed line frequency from ACpower source 102 and provides power to the motor 106. The motor 106 usedin the system 300 can be any suitable type of motor that can be poweredby a VSD 104. The motor 106 is preferably a switched reluctance (SR)motor, but can also be an induction motor, electronically commutatedpermanent magnet motor (ECM) or any other suitable motor type. Inaddition, the preferred SR motor should have a relatively flatefficiency vs. load curve. The relatively flat efficiency vs. load curveindicates that the efficiency of the SR motor does not changesignificantly with changes in the load. Furthermore, each stator phasein the SR motor is independent of the other stator phases in the SRmotor. The independent stator phases enable the SR motor to continue tooperate at a reduced power if one of the stator phases should fail.

Referring back to FIGS. 3A and 3B, the compressor 302 compresses arefrigerant vapor and delivers the vapor to the condenser 304 through adischarge line (and the reversing valve arrangement 350 if operated as aheat pump). The compressor 302 is preferably a reciprocating compressor.However, it is to be understood that the compressor 302 can be anysuitable type of compressor, e.g., rotary compressor, screw compressor,swag link compressor, scroll compressor, turbine compressor, or anyother suitable compressor. The refrigerant vapor delivered by thecompressor 302 to the condenser 304 enters into a heat exchangerelationship with a fluid, e.g., air or water, but preferably air, andundergoes a phase change to a refrigerant liquid as a result of the heatexchange relationship with the fluid. The condensed liquid refrigerantfrom the condenser 304 flows through an expansion device (not shown) tothe evaporator 306.

The condensed liquid refrigerant delivered to the evaporator 306 entersinto a heat exchange relationship with a fluid, e.g., air or water, butpreferably air, and undergoes a phase change to a refrigerant vapor as aresult of the heat exchange relationship with the fluid. The vaporrefrigerant in the evaporator 306 exits the evaporator 306 and returnsto the compressor 302 by a suction line to complete the cycle (and thereversing valve arrangement 350 if operated as a heat pump). It is to beunderstood that any suitable configuration of the condenser 304 and theevaporator 306 can be used in the system 300, provided that theappropriate phase change of the refrigerant in the condenser 304 andevaporator 306 is obtained. The HVAC or refrigeration system 300 caninclude many other features that are not shown in FIGS. 3A and 3B. Thesefeatures have been purposely omitted to simplify the drawing for ease ofillustration.

FIG. 4 illustrates an embodiment of a capacity control system 400 usedto provide capacity modulation in the compressor 304. The capacitycontrol system 400 includes the motor/VSD drive 104, as discussed above,to power the motor 106 of the compressor 302. In addition, the capacitycontrol system 400 also includes a controller or a microprocessor 402used to control the operation of the motor drive 104. In a preferredembodiment of the present invention, the controller or microprocessor402 and the motor drive 104 are integrated on a single circuit board.However, it is to be understood that the controller or microprocessor402 and the motor drive 104 can be separate from each other.

In addition, a temperature sensor 404 is used to provide a measurementof the outdoor ambient temperature to the controller or microprocessor402. The temperature sensor 404 can be any suitable device for measuringor deriving temperature and can be located in any suitable location thatcan provide an accurate determination of the outdoor ambienttemperature. Preferably, the controller 402 can be configured to controlthe output of the motor drive 104 in response to a temperaturemeasurement from the temperature sensor 404 after receiving a mode ofoperation signal, e.g., a heating mode signal or cooling mode signal,from a thermostat control or other similar device.

In another embodiment of the present invention, the controller 402 cancontrol the output of the motor drive 104 in response to other systemparameters. For example, the controller 402 can control the motor drive104 in response to measurements of condenser refrigerant pressure,evaporator refrigerant pressure, liquid line temperature, evaporatorrefrigerant temperature, condenser refrigerant temperature, suctionpressure or temperature, motor current and/or condenser air temperature.It is to be understood that the appropriate sensor is used to measurethe desired system parameter. Furthermore, the specific operation of thecontroller 402 may require modifications to accommodate a particularsystem parameter in order to provide the appropriate output capacityfrom the compressor. In still another embodiment of the presentinvention, the controller 402 can control the output of the motor drive104 in response to the temperature in the conditioned/enclosed space.

The controller or microprocessor 402 can provide the appropriate controlsignals to the motor drive 104 to control the output of the motor drive104, i.e., output voltage and output frequency from the motor drive 104.By controlling the output of the motor drive 104, the controller 402 isable to control the output speed of the motor 106 and in turn, theoutput capacity of the compressor 302. Preferably, the controller 402provides control signals to the motor drive 104 that result in one ofseveral discrete output frequencies (and corresponding voltages) beingprovided to the motor 106 by the motor drive 104. The correspondingvoltage to be provided to the motor 106 by the motor drive 104 for aparticular output frequency can be either a preset voltage that isselected to provide optimal performance or an adjustable voltage thatcan be determined by the controller 402 in response to systemconditions. The discrete output frequencies and corresponding voltagesprovided to the motor 106 result in discrete operating speeds for themotor 106 and discrete output capacities for the compressor 302.

In a preferred embodiment of the present invention, the compressor 302can be controlled and operated to have two or more discrete outputcapacities in response to an outdoor temperature measurement. Duringoperation of the system 300 in an air conditioning or cooling mode, thecompressor 302 has a first output capacity in response to the outdoortemperature being greater than a first temperature setpoint and thecompressor 302 has a second output capacity in response to the outdoortemperature being less than a second temperature setpoint. Duringoperation of the system 300 in a heating mode, the compressor 302 can beoperated at a plurality of different output capacities in response tothe outdoor temperature and, optionally, a particular stage of heatingrequired by the thermostat for the enclosed space being heated.

In one embodiment of the present invention, the system 300 is operatedin an air conditioning or cooling mode (based on a thermostat controlsignal) and the controller 402 controls the motor drive 104 to providetwo discrete output frequencies to the motor 106 depending on theoutdoor ambient temperature. In addition, the motor drive 104 canprovide the appropriate output voltage for the discrete outputfrequencies to maintain optimal motor performance. The first outputfrequency produced by the motor drive 104 is between about 35 Hz andabout 55 Hz and is initiated in response to the outdoor ambienttemperature being greater than a first temperature setpoint. However, inanother embodiment, the first output frequency produced by the motordrive 104 can be between about 70 Hz and about 120 Hz. Operating themotor 106 at the first output frequency results in the compressor 302providing a first output capacity. The first temperature setpoint can bebetween about 88° F. and about 95° F. and is preferably about 92° F.

The second output frequency produced by the motor drive 104 is betweenabout 28 Hz and about 45 Hz and is initiated in response to the outdoorambient temperature being less than a second temperature setpoint.However, in another embodiment, the second output frequency produced bythe motor drive 104 can be between about 50 Hz and about 100 Hz.Operating the motor 106 at the second output frequency results in thecompressor 302 providing a second output capacity that is lower than thefirst output capacity. The second temperature setpoint can be betweenabout 82° F. and about 88° F. and is preferably about 85° F. Inaddition, the first temperature setpoint and the second temperaturesetpoint are selected to provide a deadband region between the twotemperature setpoints. This deadband region is used to avoid frequentchanging of the output frequency of the motor drive 104 between thefirst output frequency and the second output frequency. The deadbandregion is preferably between about 2° F. and about 10° F.

The second output frequency is selected to provide a reduction incompressor output capacity, or compressor displacement, of about 15% toabout 20%, and preferably about 18%, from the first output capacity ofthe compressor 302. This reduction in capacity from operation of themotor 106 at the second output frequency occurs automatically and doesnot require any adjustment of the indoor air flow or fan speed in orderto maintain the proper amount of humidity control for the interiorspace.

The reduction in compressor capacity can increase the efficiency of thesystem 300 by providing effectively larger heat transfer surfaces (forthe corresponding refrigerant flow) in the condenser arrangement 304 andthe evaporator arrangement 306. The reduction in compressor capacity canalso provide some noise reduction for the compressor 302 because thecompressor 302 has a reduced sound signature at the lower operatingfrequencies and speed.

FIG. 5 illustrates a process for capacity modulation of the compressor302 during operation in an air conditioning mode. The process begins atstep 501 where a start-up process for the compressor is executed. Thestart-up process measures the outdoor ambient temperature with thetemperature sensor 404 and then proceeds to start-up the compressor 302to operate at the second output capacity unless the measured outdoorambient temperature is greater than or equal to the first temperaturesetpoint, then the start-up process proceeds to start-up the compressor302 to operate at the first output capacity. Next, in step 502 theoutdoor ambient temperature is measured using the temperature sensor404. In step 504, the measured outdoor ambient temperature is comparedto the first temperature setpoint to determine if the measured outdoorambient temperature is greater than or equal to the first temperaturesetpoint. If the measured outdoor ambient temperature is greater than orequal to the first temperature setpoint in step 504, then the processproceeds to step 506 where the motor 106 is operated at the first outputfrequency. The process returns to step 502 to measure the outdoorambient temperature and repeat the process. If the measured outdoorambient temperature is not greater than or equal to, i.e., it is lessthan, the first temperature setpoint in step 504, then the processproceeds to step 508. In step 508, the measured outdoor ambienttemperature is compared to the second temperature setpoint to determineif the measured outdoor ambient temperature is less than or equal to thesecond temperature setpoint. If the measured outdoor ambient temperatureis less than or equal to the second temperature setpoint in step 508,the process then proceeds to step 510 where the motor 106 is operated atthe second output frequency. The process returns to step 502 to measurethe outdoor ambient temperature and repeat the process. If the measuredoutdoor ambient temperature is not less than or equal to, i.e., it isgreater than, the second temperature setpoint in step 508, then theprocess proceeds to step 512 where the motor 106 is continued to beoperated at the current output frequency, either the first outputfrequency or the second output frequency. The process returns to step502 to measure the outdoor ambient temperature and repeat the process.

In another embodiment of the present invention, the controller 402 canalso control the motor drive 104 to provide a plurality of discreteoutput frequencies to the motor 106 during operation of the system 300in a cooling mode. The first output frequency produced by the motordrive 104 is between about 48 Hz and about 55 Hz and is initiated inresponse to the outdoor ambient temperature being less than an initialtemperature setpoint. The initial temperature setpoint can be betweenabout 88° F. and about 95° F. and is preferably about 92° F. Operatingthe motor 106 at the first output frequency results in the compressor302 providing a first output capacity. The motor drive 104 can alsoproduce a second output frequency of between about 55 Hz and about 60 Hzand in response to the outdoor ambient temperature being greater thanthe initial temperature setpoint. Operating the motor 106 at the secondoutput frequency results in the compressor 302 providing a second outputcapacity that is greater than the first output capacity.

Additional cooling mode output frequencies produced by the motor drive104 are between about 20 Hz and about 45 Hz and are initiated inresponse to the outdoor ambient temperature being progressively lowerthan the initial temperature setpoint. Operating the motor 106 at theadditional output frequencies results in the compressor 302 providingprogressively lower output capacities that are less than the firstoutput capacity. In other words, when the system 300 is operating in acooling mode, the output frequency produced by the motor drive 104 andthe corresponding output capacity of the compressor 302 areprogressively decreased as the outdoor ambient temperature progressivelydecreases below the initial temperature setpoint. In addition, thecontroller 402 (or another controller) can adjust the indoor air flow orfan speed control to accommodate changes in the output capacity of thecompressor 302. Preferably, there are one or more additional “cooling”temperature setpoints at temperatures lower than the initial temperaturesetpoint discussed above. When the outdoor ambient temperature dropsbelow these additional “cooling” temperature setpoints, the outputfrequency of the motor drive 104 is correspondingly decreased. Forexample, additional “cooling” temperature setpoints can be set at about70° F., about 75° F., about 80° F. and about 85° F. and can result inthe motor drive producing corresponding output frequencies of about 30Hz, about 35 Hz, about 40 Hz and about 45 Hz. In addition, a deadbandregion(s) can be provided between the “cooling” temperature setpointsfor the cooling mode operation to prevent frequent changing of theoutput frequency of the motor drive 104. It is to be understood that theabove temperature setpoints and corresponding frequencies are onlyexamples and any desired or suitable temperature setpoint(s) andcorresponding frequencies can be selected and used.

During operation of the system 300 in a heating mode (based on athermostat control signal), the controller 402 can also control themotor drive 104 to provide a plurality of discrete output frequencies tothe motor 106. The plurality of discrete output frequencies provided tothe motor 106 by the controller 402 in the heating mode can be relatedto the output frequencies provided to the motor 106 by the controller402 in the cooling mode. The controller 402 can use some, all, or noneof the output frequencies from cooling mode operation during heatingmode operation. In addition, auxiliary heating capacity, e.g.,resistance heating, can be engaged by the controller 402 underappropriate circumstances.

In heating mode, the controller 402 can control the motor drive 104 toprovide a plurality of discrete output frequencies to the motor 106based on the outdoor ambient temperature during operation of the system300. Each discrete output frequency of the plurality of discrete outputfrequencies is associated with an outdoor ambient temperature and isinversely related to the outdoor ambient temperature. Specifically, thehigher the outdoor ambient temperature, the lower the discrete outputfrequency that is supplied by the motor drive 104. The plurality ofdiscrete outdoor frequencies can be separated by amounts ranging fromabout 5 Hz to about 20 Hz.

In another embodiment, the selection of the discrete output frequency bythe controller 402 can be based on both the outdoor ambient temperatureand a demand for heating received by the controller 402, e.g., demandfor first stage heating, demand for second stage heating, etc. Forexample, a demand for a particular stage of heating may result in anincrease (or decrease) of the discrete output frequency that isdifferent from the output frequency that would be based on outdoorambient temperature alone. In another example, particular outputfrequencies based on corresponding outdoor ambient temperatures) mayonly be available when particular demands for heating are present. Inthis example, operation at higher output frequencies may only beavailable when a demand for second stage (higher output) heating ispresent.

In one embodiment of heating mode operation, the first output frequencyproduced by the motor drive 104 is about 30 Hz and is initiated inresponse to the outdoor ambient temperature being greater than aninitial temperature setpoint. The initial temperature setpoint can beabout 60° F. Additional heating mode output frequencies produced by themotor drive 104 are initiated in response to the outdoor ambienttemperature being progressively lower than the initial temperaturesetpoint. Operating the motor 106 at the additional output frequenciesresults in the compressor 302 providing progressively greater outputcapacities that are greater than the first output capacity. It is to beunderstood that the increase in output capacity occurs until apredetermined outdoor ambient temperature is reached. After reaching thepredetermined outdoor ambient temperature, the capacity of thecompressor begins to decrease again (assuming limitations on increasingthe drive frequency above a certain level). In other words, when thesystem 300 is operating in a heating mode, the output frequency producedby the motor drive 104 and the corresponding output capacity of thecompressor 302 is progressively increased (to a point) as the outdoorambient temperature progressively decreases below the initialtemperature setpoint.

There can be one or more additional “heating” temperature setpoints attemperatures lower than the initial temperature setpoint discussedabove. When the outdoor ambient temperature drops below these additional“heating” temperature setpoints, the output frequency of the motor drive104 is correspondingly increased. For example, additional “heating”temperature setpoints can be set at about 50° F., about 40° F., about30° F., about 20° F., about 10° F., about 0° F. and about −10° F. andcan result in the motor drive producing corresponding output frequenciesof about 35 Hz, about 45 Hz, about 60 Hz, about 80 Hz, about 100 Hz andabout 120 Hz (for temperatures of about 0° F. and below). It is to beunderstood that the above temperature setpoints and correspondingfrequencies are only examples and any desired or suitable temperaturesetpoint(s) and corresponding frequencies can be selected and used.

FIG. 7 illustrates the difference in compressor capacity in the heatingmode when operating the compressor at a single stage capacity, i.e.,using a fixed frequency, versus operating the compressor at variablecapacities, i.e., using variable frequencies as discussed above. Inaddition, a deadband region(s) can be provided between the “heating”temperature setpoints for the heating mode operation to prevent frequentchanging of the output frequency of the motor drive 104. For example,once a discrete output frequency has been selected by the controller402, it is not changed until another outdoor ambient temperaturesetpoint has been passed.

FIG. 6 illustrates a process for capacity modulation of the compressor302 during operation in a heating mode. The process begins at step 601where a start-up process for the compressor is executed. The start-upprocess receives a first stage heating signal and then proceeds tostart-up the compressor 302 to operate at a predetermined start-upfrequency and corresponding output capacity. Next, in step 602 theoutdoor ambient temperature is measured using the temperature sensor404. In step 604, the controller 402 determines if an optional secondstage heating demand has been made. If a second stage heating demand hasbeen received in step 604, then the process proceeds to step 608. If asecond stage heating demand has not been received in step 604, then theprocess proceeds to step 606 where the motor 106 is operated at apredetermined output frequency based on the measured outdoor ambienttemperature. The process returns to step 602 to measure the outdoorambient temperature and repeat the process.

In step 608, the operating frequency of the motor 106 is compared to apredetermined operating frequency to determine if the operatingfrequency of the motor is less than the predetermined operatingfrequency. If the operating frequency of the motor is less than thepredetermined operating frequency in step 608, the process then proceedsto step 610 where the motor 106 is operated at the predeterminedoperating frequency. The process returns to step 602 to measure theoutdoor ambient temperature and repeat the process. If the measuredoutdoor ambient temperature is not less than, i.e., it is greater thanor equal to, the predetermined operating frequency in step 608, then theprocess proceeds to step 612 where the motor 106 is operated at apredetermined output frequency based on the measured outdoor ambienttemperature. The process returns to step 602 to measure the outdoorambient temperature and repeat the process.

In another embodiment of the present invention, step 608 can be replacedby a step that determines whether the controller has received the secondstage heating demand for the first time. If the second stage heatingdemand has been received for the first time, step 610 is replaced by astep where the controller 402 can increase the frequency of the motor bya step or frequency increment, as discussed above, that can be suppliedto the motor, e.g., from 45 Hz to 50 Hz. The process then returns tomeasure the outdoor ambient temperature. If it is not the first time thesecond stage heating demand has been received, the process would proceedto step 612 as described above with respect to FIG. 6.

In a preferred embodiment of the present invention, the controller 402is programmable by a user. A user either at the factory (beforeinstallation) or in the field (during or after installation) can programthe controller 402 to set the desired operating frequencies, e.g.,first, second, etc., in both the heating mode and the air conditioningor cooling mode. In addition, a user can configure the controller to setdesired temperature setpoints and deadband regions for both the heatingmode and the air conditioning mode. By being programmable, thecontroller 402 is able to be adjusted to operate the compressor 302 inaccordance with particular system configurations and conditions (e.g.,condenser and/or evaporator coil size or surface area, amount and typeof refrigerant charge, and condenser and/or evaporator airflow) toprovide a desired system performance. The programmability of thecontroller 402 (and compressor 302) may remove the need to change oralter other system components to obtain a desired system performancesuch that the desired system performance can be obtained by adjustingonly the controller 402. The controller 402 can be programmed only onetime or can be programmed and erased multiple times. The programmabilityof the controller 402 enables a single controller/compressor combinationto be used with a variety of different types of refrigeration systemconfigurations and still provide a desired system performance for eachof the systems.

For example, the controller 402 can provide initial output frequenciesand initial output voltages. The initial output frequencies arepreferably set to initial predetermined frequencies and the initialoutput voltages can either be set to an initial predetermined voltagesor can be determined and set by the controller 402 as discussed above.Next, the particular system configurations and conditions for the HVAC&Rsystem into which the controller 402 and compressor 302 are going to beinstalled are determined. The initial predetermined frequency values forone or more of the initial output frequencies and possibly one or moreof the initial output voltages can be adjusted in response to thedetermined system configurations and conditions. The HVAC&R system isthen tested with the output frequencies and the output voltages, asadjusted, to determine the performance of the HVAC&R system. One or moreof the output frequencies can be further adjusted and possibly one ormore of the output voltages can be further adjusted in response to thedetermined system performance not being the desired system performance.Finally, the testing of the HVAC&R system and the adjusting of one ormore of the output frequencies and possibly one or more of the outputvoltages can be repeated until the desired performance for the HVAC&Rsystem is obtained.

In another embodiment of the present invention, the controller 402 canbe used to provide overload and underload protection to the motor 106.The controller 402 can measure the current being provided to the motor106 by the motor drive 104 with respect to the outdoor ambienttemperature measured by the temperature sensor 404 and can takecorrective action if an overload or underload condition is present inthe motor 106 or motor drive 104. Specifically, there will be a directrelationship between the measured motor current and the outdoor ambienttemperature that determines if an overload or underload condition ispresent. For example, an overload condition can be determined to bepresent by exceeding a predetermined outdoor temperature for a specificmotor current value.

In still another embodiment of the present invention, an override signalcan be provided to override the capacity modulation process set forthabove. The override signal can be used to force the operation of themotor 106 at a particular output frequency instead of operating themotor 106 at the selected output frequency in accordance with signalsfrom the capacity modulation process. The override signal can begenerated by a thermostat or other control device or can be provided asa direct or manual input by a user of the system 300. For example, theoverride signal can be used to provide additional or boosted coolingcapacity from the compressor 302 during cooling mode operation, i.e.,the compressor 302 can be operated at the first output capacity insteadof the second output capacity, when other conditions and factors takeprecedence over the lower outdoor ambient temperature control of thecapacity modulation process set forth above.

If the temperature in an enclosed space to be cooled is greater than thetemperature setpoint for the enclosed space by a predetermined amountand the capacity modulation process is operating the compressor 302 atthe second output capacity, the capacity modulation process isoverridden and the compressor 302 is operated at the first outputcapacity. The override control provided by the override signal can befor a predetermined override time period, e.g., 1 hour, or the overridecontrol can continue until the condition that triggered the overridesignal is satisfied, e.g., satisfaction of a temperature setpoint for anenclosed space. Once the override control has ended, the capacitymodulation process resumes control of the operation of the compressor302. In another embodiment, the controller 402 can initiate the overridecontrol in response to system conditions, e.g., extended operation atthe lower output capacity in either heating or cooling mode ofoperation. The override control in this embodiment can be terminated asdiscussed above, i.e., satisfaction of a predetermined time period or ofthe temperature setpoint for the enclosed space.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A method for modulating capacity in a compressor for a heat pumpoperating in a heating mode, the method comprising: providing acontroller configured to provide a plurality of discrete outputfrequencies to a motor for the compressor of the heat pump; measuring anoutdoor ambient temperature; selecting a discrete output frequency ofthe plurality of discrete output frequencies in response to the measuredoutdoor ambient temperature; operating the motor at the selecteddiscrete output frequency and a corresponding voltage to produce acorresponding output capacity for the compressor; and wherein theselected discrete output frequency of the plurality of discrete outputfrequencies is inversely related to the measured outdoor ambienttemperature.
 2. The method of claim 1 further comprising repeating thesteps of measuring an outdoor ambient temperature, selecting a discreteoutput frequency, and operating the motor at the selected discreteoutput frequency until a demand for heating is satisfied.
 3. The methodof claim 1 further comprising the step of executing a start-up processfor the compressor, the step of executing a start-up process for thecompressor includes: receiving a first stage heating signal indicating ademand for heating; and operating the motor at a predetermined startupfrequency and a corresponding voltage to produce a corresponding outputcapacity for the compressor.
 4. The method of claim 1 furthercomprising: determining whether a demand for additional heating ispresent; and executing the steps of selecting a discrete outputfrequency and operating the motor at the selected discrete outputfrequency in response to no demand for additional heating being present.5. The method of claim 4 further comprising the step of: determiningwhether an operating frequency for the motor is less than apredetermined frequency in response to a demand for additional heatingbeing present; executing the steps of selecting a discrete outputfrequency and operating the motor at the selected discrete outputfrequency in response to the operating frequency for the motor beinggreater than the predetermined frequency; and operating the motor at thepredetermined frequency in response to the operating frequency for themotor being less than a predetermined frequency.
 6. The method of claim4 further comprising the step of: determining whether the demand foradditional heating has been present more than one time in response to ademand for additional heating being present; executing the steps ofselecting a discrete output frequency and operating the motor at theselected discrete output frequency in response to the demand foradditional heating being present more than one time; and selecting adiscrete output frequency of the plurality of discrete outputfrequencies greater than an operating frequency of the motor in responseto the demand for additional heating being present one time.
 7. Themethod of claim 6 wherein the step of selecting a discrete outputfrequency of the plurality of discrete output frequencies greater thanan operating frequency of the motor includes selecting a next greaterdiscrete output frequency of the plurality of discrete outputfrequencies.
 8. The method of claim 1 wherein each discrete outputfrequency of the plurality of output frequencies has a correspondingpredetermined temperature setpoint.
 9. The method of claim 8 furthercomprising the step of programming, by a user, at least one of theplurality of discrete output frequencies or the correspondingpredetermined temperature setpoints for the plurality of discrete outputfrequencies.
 10. The method of claim 8 wherein: the plurality ofdiscrete output frequencies includes at least two discrete outputfrequencies selected from the group consisting of about 35 Hz, about 45Hz, about 60 Hz, about 80 Hz, about 100 Hz and about 120 Hz; and thecorresponding predetermined temperature setpoints for the plurality ofdiscrete output frequencies includes at least two predeterminedtemperature setpoints selected from the group consisting of about 50°F., about 40° F., about 30° F., about 20° F., about 10° F. and about 0°F.
 11. The method of claim 8 wherein the corresponding predeterminedtemperature setpoints progressively decrease in response to the discreteoutput frequencies progressively increasing.
 12. The method of claim 1wherein the plurality of discrete output frequencies are separated by atleast 5 Hz.
 13. An HVAC&R system comprising: a compressor, a condenserarrangement and an evaporator arrangement connected in a closedrefrigerant loop; a motor connected to the compressor to power thecompressor, the motor being configured to operate at a plurality ofoutput speeds to generate a plurality of output capacities from thecompressor; a control system, the control system being configured toprovide the motor with a plurality of discrete output frequencies togenerate the plurality of output speeds in the motor; a sensorarrangement to measure a parameter corresponding to an outdoor ambienttemperature and to provide a signal to the control system with themeasured parameter; and wherein, in response to the HVAC&R systemoperating in a heating mode, the control system being configured toprovide a discrete output frequency of the plurality of discrete outputfrequencies to the motor in response to the measured parameter, theprovided discrete output frequency being increased in response to adecrease in the outdoor ambient temperature to generate an increase inthe output capacity of the compressor.
 14. The HVAC&R system of claim 13wherein the sensor arrangement is a temperature sensor and thetemperature sensor is configured to measure the outdoor ambienttemperature.
 15. The HVAC&R system of claim 13 further comprising athermostat, the thermostat being configured to provide one of a firststage heating signal or a second stage heating signal to the controlsystem, and wherein a second stage heating signal indicates a greaterdemand for heating than a first stage heating signal.
 16. The HVAC&Rsystem of claim 15 wherein the control system is configured to provide adiscrete output frequency of the plurality of discrete outputfrequencies to the motor greater than an operating frequency of themotor to generate an increase in the output capacity of the compressorin response to receiving a second stage heating signal for a first time.17. The HVAC&R system of claim 13 wherein each discrete output frequencyof the plurality of output frequencies has a corresponding predeterminedtemperature setpoint.
 18. The HVAC&R system of claim 17 wherein at leastone parameter selected from the group consisting of the plurality ofdiscrete output frequencies and the corresponding predeterminedtemperature setpoints for the plurality of discrete output frequenciesis programmable by a user.
 19. The HVAC&R system of claim 17 wherein:the plurality of discrete output frequencies includes at least twodiscrete output frequencies selected from the group consisting of about35 Hz, about 45 Hz, about 60 Hz, about 80 Hz, about 100 Hz and about 120Hz; and the corresponding predetermined temperature setpoints for theplurality of discrete output frequencies includes at least twopredetermined temperature setpoints selected from the group consistingof about 50° F., about 40° F., about 30° F., about 20° F., about 10° F.and about 0° F.
 20. The HVAC&R system of claim 13 wherein the pluralityof discrete output frequencies are separated by at least 5 Hz.
 21. TheHVAC&R system of claim 13 wherein the control system comprises: a motordrive connected to the motor; and a controller, the controller beingconfigured to receive the signal with the measured parameter, determinethe provided discrete output frequency and provide control signals tothe motor drive to operate the motor at the provided discrete outputfrequency.
 22. The HVAC&R system of claim 13 wherein the compressor is areciprocating compressor and the motor is a switched reluctance motor.23. A method for controlling capacity in a compressor of an HVAC&Rsystem, the method comprising: providing a controller configured toprovide a plurality of discrete output frequencies to a motor for thecompressor; measuring an outdoor ambient temperature; determiningwhether the HVAC&R system is operating in a heating mode or a coolingmode; in response to the HVAC&R system operating in a heating mode,executing a heating mode operation process comprising: selecting adiscrete heating mode output frequency of a plurality of discreteheating mode output frequencies in response to the measured outdoorambient temperature; operating the motor at the selected discreteheating mode output frequency and a corresponding voltage to produce acorresponding output capacity for the compressor; and wherein theselected discrete heating mode output frequency of the plurality ofdiscrete heating mode output frequencies progressively increases inresponse to the measured outdoor ambient temperature decreasing toprovide an increase in the output capacity of the compressor; and inresponse to the HVAC&R system operating in a cooling mode, executing acooling mode operation process comprising: comparing the measuredoutdoor ambient temperature to at least one predetermined temperaturesetpoint; selecting a discrete cooling mode output frequency of aplurality of discrete cooling mode output frequencies based on thecomparison of the measured outdoor ambient temperature and the at leastone predetermined temperature setpoint; operating the motor at theselected cooling mode discrete output frequency and a correspondingvoltage to produce a corresponding output capacity for the compressor;and wherein the selected discrete cooling mode output frequency of theplurality of discrete cooling mode output frequencies progressivelyincreases in response to the measured outdoor ambient temperatureincreasing to provide an increase in the output capacity of thecompressor.
 24. The method of claim 23 wherein the plurality of discreteoutput frequencies includes the plurality of discrete heating modeoutput frequencies and the plurality of discrete cooling mode outputfrequencies.
 25. The method of claim 24 wherein the plurality ofdiscrete output frequencies are separated by at least 5 Hz.
 26. Themethod of claim 24 wherein the plurality of discrete heating mode outputfrequencies are different from each discrete cooling mode outputfrequency of the plurality of discrete cooling mode output frequencies.27. The method of claim 24 wherein the plurality of discrete heatingmode output frequencies includes at least one discrete cooling modeoutput frequency of the plurality of discrete cooling mode outputfrequencies.
 28. The method of claim 23 wherein: the step of comparingthe measured outdoor ambient temperature to at least one predeterminedtemperature setpoint includes: comparing the measured outdoor ambienttemperature to a first predetermined temperature setpoint; and comparingthe measured outdoor ambient temperature to a second predeterminedtemperature setpoint; and the step of selecting a discrete cooling modeoutput frequency of the plurality of discrete cooling mode outputfrequencies includes: selecting a first cooling mode output frequencyand corresponding voltage in response to the measured outdoor ambienttemperature being greater than the first predetermined temperaturesetpoint; and selecting a second cooling mode output frequency andcorresponding voltage in response to the measured outdoor ambienttemperature being less than or equal to the second predeterminedtemperature setpoint.